Process of bleaching starch



, periods of storage.

Patented Feb. 29, 194.4.

raoonss or BLEACIIING s'raacu om n. Eble and Monroe J. Mason, St. Louis, Mo., assignors to Anheuser-Busch, Incorporated, St. Louis, Mo a corporation of Missouri No Drawing. Application August 3,1940.

p Serial n 351,201

7 Claims.

This invention relates to the manufacture of starch and particularly to the bleaching thereof. In the usual method of manufacturing starch,

it is common practice to use chlorine gas. chlorine water or a hypochlorite as a bleaching agent; but the starch thus produced is. liable to have a gray or pink or greenish tinge, and the starch is liable to undergo some modification and a paste made from such starch will have a lower viscosity than natural starch. The object of the present invention is to produce a clear white starch, that'is substantially unmodified, and whose viscosity is substantially equal to the viscosity of natural starch and which will be stable throughout long 'tion of sodium hypochlorite in water containing about twelve per cen't of available chlorine is used, which is equivalent to about .04 per cent chlorine on the dry substance starch.

, In carrying out this operation, the temperature of the starch liquor is kept in the neighborhood of 120 to 125 degrees Fahrenheit; and the operation is continued for say an hour. In a typical The invention consists principallyiin using a salt of chlorous acid in connection with chlorine or a hypochlorite as hereinafter described. It also consists in the steps and combinations of steps hereinafter described and claimed.

My invention is particularly adapted for pro-- -ducing clear white corn starch and thefollowin applied to the is i r ption of my process as manufacture of corn starch.

In the commercial production of starch from com, the crude starch is suspended in water and filtered. The moist starch is washed by again suspending it in water and filtering and this operation may be repeated several times dependin upon the amount of solubles contained in the original crude starch and the degree of refinement desired. Following the second or later washins, the moist starch is suspended in such amount of' water as to obtain a starch liquor preferably of about degrees Be'aum.

Solutions of sodium chlorite and of sodium'hy pochlorite are added to the starch liquor in suitable quantity. For instance, a sufiicient quantity of this. starch liquor is used to represent, say 7500 pounds of dry substance starch. The sodium chlorite and sodium hypochlorite ar issolved in water, preferably in separate tanks each of which is provided with a valved outlet pipe and these pipes are connected to form a single feed pipe for delivering the mixture of the two solutions into the main tank that contains the starch and which is provided with a suitable mechanical stirring device for keeping the starch in suspension and for adequately mixing the solutions with the starch liquor. For 7500 pounds of dry substance starch, about seven and one-half pounds of sodium chlorite are used, which is equivalent to about .10 per cent of sodium chlorit on the dry substance starch. For this same amount of starch, about two and one-half gallons of a solucase, the hydrogen ion concentration is approximately between pH 4.5 and pH 5.0. At the end of this operation, the starch is washed, filtered and dried in any well known manner.

The starch produced as hereinbefore described has a clear white color, is unmodified to any appreciable extent, is stable over long periods of storage, and a paste made therefrom has substantially the same viscosity as the starch before bleaching. Accordingly thestaroh thus produced is well adapted for such uses as sizing high grade paper and other purposes where a clear vwhitesize 0r starch is requisite and for food products where stability and viscosity value are important.

While I have described a typical example of my process as applied to the bleaching of corn starch, it is noted that the process is applicable to the bleaching of other starches and that it is not limited to the particular reagents and conditions specified. For instance, calcium chlorite or any other salt of chlorous acid may be substituted for sodium chlorite, but, on account of chlorous acid itself being unstable and dangerous, it is not considered suitable for practical use. Likewise, chlorine, chlorine water, calcium hypochlor'ite or any other hypochlorlte may be substituted for sodium hypo hlorite. Allthe members of this last mentioned group are chlorine or yield chlorine as the active bleaching agent; and

they are all so vigorous in their action that they are liable to overoxidize the starch, cause discoloration and modification thereof and vary the viscosity of its paste. On the other hand, the members of the first group, namely the chlorites or salts of chlorous acid, act too weakly when used alone. When, however, members of the two groups are used conjointly, they produce remarkably satisfactory bleaching effects without appreciably impairing the desired qualities of the starch.

-In the specific example stated, the temperature of the starch liquor is specified as from about to about degrees Fahrenheit. .A higher temperature is permissible but ordinarily would not be desirable if it'added to the cost. On the other hand, the operation may be carried out at a temperature as low as 85 degrees Fahrenheit.

the bleaching operation is specified as about one hour. This time could have been prolonged to as much as three or four hours under the conditions specified without destructive effect on the starch. The'time might also have been shortened to less than an hour under the conditions specified, al- 10 though, in the average case, it is not desirable to shorten the period to less than one-half hour.

In the specific example given, the hydrogen ion concentration of the starch liquor is specified as between pH 4.5 and pH 5.0. This range may beextended to from pH 4.0 to pH 7.0. If the operation of the starch manufacturing process is such as to yield a starch liquor that is not within the desired hydrogen ion concentration range, it may be brought within said range by adding any suitable acid, such as sulphuric or hydrochloric acid. or alkaline material, such as sodium carbonate or caustic soda, as conditions may require.

If it is desired to produce a finished dry starch which would have a pH value of say 5.5, the proper amount of a suitable alkaline agent, such as reagents being added prior to thelast washing. :5

In such cases, the amount of bleaching agents which are applied during the first stage is approximately, or slightly more than, one-half of the total amount of reagents required in a single batch bleaching, and a similar amount is used 40 in a subsequent bleaching operation. .Whether the bleaching process is conducted as a single bleach or in separate stages, it is advantageous to use the filtrate from such bleached starch liq uor 'as fluid for the suspension of crude starch 4 or other mill house fractions. Thus, all the available bleaching acting will be utilized at some stage in the refining process.

The proportion of available chlorine derived from the chlorite to the chlorine derived from chlorine or a chlorine-yielding compound may be varied. While the active chlorine may be 25 to 75 per cent of that derived from the chlorite salt, it is preferable touse an amount of active available chlorine, whether supplied as chlorine or yielded by the hypochlorite salt, which is equal to 25 to per cent of the chlorine yielded by the chlorite.

What we claim is:

1. The process of bleaching starch which com- 60 prises subjecting the starch. while in suspension in starch liquor having a hydrogen ion concentration value between pH 4 and pH '7 and at a temperature between degrees Fahrenheit and 2; The process or bleaching starch which comprises subjecting the starch. while in suspension and at a temperature high enough to bleach the starch without appreciably modifying it. to the action of chlorine in the presence of a salt oi chlorous acid, the weight oi said salt being about one tenth of one percent of the weight of the starch dry and the weight of the chlorine being about four-hundredths of one percent of the weight of the starch dry. v

3. The process oi bleaching starch which comprises subjecting the starch, while in suspension and at a temperature high enough to bleach the starch and low enough to prevent appreciable modification thereof. to the action of sodium hypochlorite in the presence of sodium chlorite. the weight of said sodium chlorite being about one tenth of one percent of the weight of the starch dry and the weight of the chlorine derived from sodium hypochlorite being about four-hundredths of one percent of the weight of the starch dry.

4. The process of bleaching corn starch which consists in subjecting it, while in suspension in starch. liquor having a hydrogen ion concentration value between pH 4 and pH 7 and a temperature between 85 and 125 degrees Fahrenheit. to the simultaneous action of a salt of chlorous acid and a member or the group consisting of chlorine. hypochlorite of sodium and hypochlorite of calcium, using the salt of chlorousacid at the rate of aboutone tenth of one percent of the weight of the starch dry and using enough of said group member to yield chlorine equivalent to iour-hundredths of one percent of the weight of the starch dry.

5. The process of bleaching corn starch which consists in subjecting it, while in suspension in starch liquor having a hydrogen ion concentration value between pH 4.5 and pH 5 and a temperature of approximately 120 to 125 degrees Fahrenheit. to the simultaneous action of a salt of chlorous acid and a member oi. the group consisting of chlorine, hypochlorite of sodium and hypochlorite of calcium, using the salt of chlorous acid at the rate of about one tenth 01' one percent of the weight of the starch dry and using enough of said group member to yield chlorine equivalent to four-hundredths of one percent of the weight of the starch dry.

6. The process of bleaching starchwhich comprises subjecting the starch for a period of from about one half hour to about four hours, while the starch is in suspension in starch liquor having a hydrogen ion concentration value between pH 4 and pH 7 and at a temperature between 85 degrees Fahrenheit and 125 degrees Fahrenheit. to the action of chlorine in the presence of a salt of chlorous acid.

'7. The process of bleaching starch by subjecting the starch in an aqueous medium to the action of sodium chlorlte in an amount 01' about 0.10 per cent of the dry weight of the starch and a minor proportion of a hypochlorite. of a pH of about 4 to 6 and at a temperature of about 125 degrees Fahrenheit, to theaction of a hy o- 66 F.

chlorite salt in the presence of a salt of chlorous acid.

o'rro H. EBLE. MONROE .1. MASON. 

